Ultrafast spectroscopic studies of photoinduced electron transfer from semiconducting polymers toC60

Using femtosecond time-resolved photoinduced absorption spectroscopy, we have studied the dynamics of photoinduced electron transfer from semiconducting polymers to ${\mathrm{C}}_{60}$. We find that with ${\mathrm{C}}_{60}$ in poly[2-methoxy-5-(2’-ethyl-hexyloxy)-p-phenylene vinylene)], poly(2,5-bis(cholestanoxy)-1,4-phenylene vinylene), and poly(3-octylthiophene) (P3OT), ultrafast photoinduced electron transfer occurs from the ${\mathrm{\pi }}^{\mathrm{*}}$ band of the semiconducting polymer to the lowest unoccupied molecular-orbital level of ${\mathrm{C}}_{60}$. Time-resolved measurements of the dichroic ratio place a 300-fs upper limit on the electron transfer time. The charge-separated state is rendered metastable due to the spatial separation of the electron and hole and to polaron formation associated with the electron on the ${\mathrm{C}}_{60}$ and the hole on the semiconducting polymer. Increasing the ${\mathrm{C}}_{60}$ concentration in P3OT increases the lifetime of the charge-separated state. The two p-phenylene vinylene derivatives also displayed metastable charge separation.